Joint for concrete slabs



July 1, 1-930.

.8. F. FRIBERG- v JOINT FOR CONCRETE SLABS Filed April 15 1929 MM 5 TE Nw/ n. a v E J. V. B

Patented July 1, 1930 mm STTES BENGT F. FRIEBERG, OF ST. LOUIS, MISSOURI, ASSIGNOR TO LACLEDE STEEL COMPANY, OF ST. LOUIS, MISSOURI, A CORPORATION OF MISSOURI JOINT FOR CONCRETE SLABS Application filed April 15,

This invention relates generally to concrete pavements-and more specifically to improved means for controlling the lines of fracture occurring in the surfaces of such structures, the predominant object of the invention being to' provide means adapted to be embedded in a concrete pavement which will cause the pavement to crack along a predetermined line if for some reason tensional stresses in the concrete slab exceed the,

strength of the concrete itself;

The invention also relates to a joint of the class referred to which is so constructed and arranged in the concrete slab that alinement 5 of the parts of the pavement at opposite sides of a crack occurring at the joint is assured.

It is a known fact that concrete pavements exposed to the air will be subject to quite sub stantial temperature stresses, causing the pavement to crack at intervals. It is not possible by known means to prevent these cracks, and in the absence of such means it is desirable to cause them to follow along certain lines, thus dividing the pavement into lanes or squares.

Prior to this invention joints have been embedded in the concrete of the pavement for the purpose of controlling the location of these cracks or fractures, and among the joints so employed is one which divides the pavement completely, or almost completely,

into parts. The joints of this type either extended straight down through the slab, in

which case no interlocking of the parts of the pavement at opposite sides of the joint was obtained, or said joint was provided with one or more corrugations for interlocking the parts of the pavement at opposite sides of the oint. The disadvantage of this type of joint is that the pavement is divided at locations where no separation is really necessary,

namely, at the approximate vertical centers of the slabs, and at which locations free communication between the adjoining parts of 4 the pavement is desirable for a proper construction of the pavement.

Another method of controlling the lines of fractures in concrete pavements involves producing a groove in the surface of the pavement whereby a plane of weakness is 1929. Serial No. 355,055.

efl'ected. The groove referred to, which is usuallyifilled with asphalt, is made with a tool and the interlocking of the adjoining parts of the pavement is insured by the irregularity of the line of fracture below the bottom of the groove. The disadvantage of this method is that the interlocking is sufficient in places where the general direction of the crack is vertical, but it is not sufficient should the fracture occur along a sloping plane from the bottom of the groove to the bottom surface of the slab.

The main purpose of the improved joint construction disclosed herein is to eliminate the disadvantages referred to above, and briefly stated, said joint comprises a pair of strips of non-elastic material located at the top and bottom portions, respectively, of the concrete slab. The strips referred to are separated by a free space therebetween through which concrete may pass freely when theroadway is being laid. My improved joint also includes other details of construction and arrangement in the roadway which serve to render said joint superior to the elements heretofore em loyed for its purpose, and these details 0 construction and arrangement will be fully disclosed herein.

Fig. 1 is a fragmentary sectional perspec tive of a roadway having my improved joint associated therewith.

Fig. 2 is a cross-section taken through the roadway and joint shown in Fig. 1.

Fig. 3 is a fragmentary cross-section taken through a roadway having another form of myimproved joint associated therewith.

Fig. 4 is a view similar to Figs. 2 and 3, but illustrating a third form of the invention.

In the drawing, wherein is shown for purposes of illustration merely several forms of the invention, and referring particularly to Fig. 1 thereof, A designates a concrete roadway which may be constructed in the usual manner and rests upon the ground B. C designates one of my improved joints, said joint being extended along the pavement in a line where a crack, should such occur, may be conveniently provided for.

Referring now to the improved joint C, said joint comprises an element composed of a pair of strips 1 and 2 formed of suitable material which are separated from each other in a vertical direction to provide a space 3 therebetween. Although they are not entirely essential, I prefer to arrange connecting portions 4, which serve to connect the upper strip 1 and the lower strip 2'together. The connecting portions 4 may be formed integrally. with the strips 1 and 2, or may, if desired, be .separate elements secured thereto, and said connecting portions are arranged substantially vertically and a space of considerable extent is provided between each adjacent pair of such portions, as shown clearly in Fig. 1.

, In the production of a road having one of my improved joints associated therewith, the

lower strip will rest upon the ground, as suggested in Fig. 1, or will be located near the ground, and the upper strip will be positioned so that its top edge will be located-a short distancebelow the surface of the pavement.

The upper and lower strips of the joint C -will be supported in a substantially vertical position by suitable means, such as stakes which, if desired, may be driven into the ground. The concrete of which the roadway 39 is comprised is then placed in position in the usual manner, said concrete flowing from one side of the roadway to the other through x the space 3 between the strip portions 1 and 2 and between the spaced connecting porv tions 4, when present. Also, the provision of a joint with an open web gives full freedom to the user of the joint for extending such material as dowels or reinforcement from one part of the pavement to an adjoining'part thereof. Because the top edge of thej'strip portion 1' is spaced downwardly from the surface of the roadway, there will be no indication at the surface of the roadeureat the plane of weakness created by the joint and the crack will be controlled as to its location at the two strips of the joint! In order words, the crack at the surface of the roadway will follow the upper edge of the upperTstrip and will therefore be substantially straight, and the crack through the portion of the concrete body between the strip 1 and the strip 2 'will be irregular, as indicated in the drawing, so as to provide to e portionson the slab portions at opposite sides of the crack capable of interlocking with each other to prevent vertical dis- 7 placement of'the slab portions relative to each other. a To provide my strip with the required ture of the pavement, such fracture will ocrigidity I may if desirable arrange an offset flange 6 at the bottom edge of the upper strip portion land a similar flange 7 at the top strip opposite from the side from which the flange 7*.extends, as shown in Fig. 4. Also, if desired the flanges 6 and 7 between one adjacent pair of connecting portions 4 may be extended in a direction opposite from that in which the flanges 6 and 7 between the' next adjacent pairof connecting portions extend, as suggested in Fig. 1.

' As already stated, it is not absolutely essential that my improved joint be provided with the connecting portions 4, and when.

they are omitted, as shown in Fig. 3, the separate strips 1 and 2 will be maintained in their proper vertical positions during production of the roadway by suitable supporting means. Also, when the connecting portions are not employed the flanges 6 and ,7 may be made continuous from end to end of the strip portions, if desired, and when connecting portions are employed suitable strengthening ribs, such as those designated in Fig. 1 by the reference character 4', may be provided to give the joint sufficient stiffness to allow its handling before it has reached its place in the road slab. These strengthening ribs are extended longitudinally of the'joint and preferably overlap the portions of the joint adjacent to the connecting portions 4. Also, to provide additional strength transversely of the connecting portions 4, I employ the outwardly extended flanges 4 which are located at opposite ends of said connecting portions and extend transversely of the joint.

By predetermining the location of the; crack at the bottom as Well as at the top of the concrete pavement by strips arranged in a vertical plane as described, the extension of the crack along a sloping plane through the slab is prevented, and complete interlocking of the parts of the slab is insured by the irregularity of fracture between the two strips. Also, v by arranging the two strips of the joint close to the top and bottom surfaces of the slab where the greatest stresses due to temperature changes occur, and where the cracks will be-initiated, it is quite evident that the controlling of the location of the crack will be more completely assured with a lesser amount of material 7 than if'these strips, as heretofore, should extend through the center portion of the slab.

It is to be noted that the-flanges 6 and 7 do not, in any sense, serve to interlock the slab portions at opposite sides of the joint. to-

I claim: I

1. In combination with a body of concrete or like material constituting a slab of a roadway or similar structure, a crack-locating element embedded in the body of concrete immediately adjacent to thetop surface thereof and arranged to inducea crack occurring in the'roadway slab to be located in a predetermined position, and a second element embedded in the body of concrete adjacent to the bottom thereof, the first and second mentioned elements being of like characteristics and being separated from each other in a vertical direction to provide a free space therebetween, said first and second mentioned elements constituting permanent parts of the concrete structure and the free space therebetween being so located and proportioned as to induce said body of concrete or like'material to crack at said free space.

2. In combination with a body of concrete or like material constituting a slab of a roadway or similar structure, a crack-locating element embedded in the body of concrete immediately adjacent to the top surface thereof,-

and-arranged to induce a crack occurring in the roadway slab to be located in a predetermined position, a second element embedded in the body of concrete adjacent to the bottom thereof, the first and second mentioned elements being of like characteristics and being separated from each other in a vertical direction to provide a free space therebetween, said first and second mentioned elements constituting permanent parts of the concrete structure and the free space therebetween being so located and proportioned as to induce said body of concrete or vlike material to crack at said free space, and means arranged on said elements for addingstrength thereto. j

3. In combination with a body of concrete or like material constituting a slab of a roadway or similar structure, a crack-locating element embedded in the body of concrete immediately adjacent to the top surface thereof and arranged to induce a crack occurring in the roadway slab to be located in a predetermined position, a second element embedded in the body of concrete adjacent to the bottom thereof, the first and second mentioned elements being of like characteristicsand being separated from each other in a vertical direction to provide a free space therebetween which is so located and proportioned as to induce said body of concrete or like material to crack at said free space, and connecting portions for connecting said separated elements together.

4. In combination with a body of concrete or like material constituting a slab of a roadway or similar structure, an element embedded in the body .of concrete immediately adjacent to the top surface thereof, a second element embedded in the body of concrete adjacent to the bottom thereof, the first and second mentioned elements being of like characteristics and being separated from each other in a vertical direction to provide a free space therebetweenwhich is so located and proportioned as to induce said body of element embedded in the body of concrete adjacent to the bottom thereof, the first and second mentioned elements being of like characteristics and being separated from each other in a'vertical direction to provide a free space therebetween, said first and second mentioned elements constituting permanent parts of the concrete structure and the free space therebetween being so located and proportioned as to induce saidbody of concrete or like material to crack atsaid free space, connecting portions for connecting said separated elements together, said connecting portions being spaced longitudinally of the-first and second mentioned elements, and means arranged on the first and second i mentioned elements for adding strength thereto. j

6. In combination with a bodyiof concrete or like material constituting a slab of a roadway. or similar structure, a strip of material embedded in the body of concrete immediately adjacent to the top surface thereof, a second strip of material embedded in the body of concrete adjacent to the bottom thereof, the first and second mentioned strips of ma terial being of like characteristics and being separated from each other in a vertical direction to provide a free space therebetween, said first and second mentioned strips constituting permanent'parts of the concrete structure and the free ,space therebetween being so located and proportioned as to induce said body ofconcrete or like material to crack at said free space, connecting portions for connecting said separated strips together, said connecting portionfs being spaced longitudinally of the first and'second mentioned strips, and outwardly extended flange elements arranged on the first and second mentioned characteristics and being separated from each other in'a vertical direction to provide a free space therebetween, said first and second mentioned elements constituting permanent 5 parts of the concrete structureand the free space therebetween being so located and proportioned as to induce said body of concrete or like material to crack at said free space, connecting portions spaced longitudinally of the first and second mentioned elements for 7 connecting said elements together, and strengthening elements for adding rigidity to said connecting portions. I

8. In combination with a body of concrete 5 or like material constituting a slab of a roadway or similar structure, an element embedded in the body of concrete immediately adjacent to the top surface thereof, a second element embedded. in the body of=concrete adjacent to the bottom thereof, thefirst and second mentioned elements being I of like i characteristics and being separated from each other in a vertical direction to provide a free space therebetween, said first and sec-' 0nd mentioned elements constituting permanent parts of the concrete structure and the free space therebetween being so located and proportioned as to induce said body of concrete or like material to crack at 'said free space, connecting portions spaced longitudinally of the first and second mentioned elements for connecting said elements together, and strengthening elements extended longitudinally and transversely of the connectin portions for addingrigidity thereto.

9. A joint for roadway slabs, comprising a crack-locating element adapted to be embedded in a body of concrete constituting a slab of a roadway or similar structure imme:

40 diatelyadjacent to the top surfacethereof,

and a second element adapted to be embedded in the body of concrete adjacent to the bottom thereof, the. first and second mentioned elements being of like characteristics and'being separated from each other in a vertical di- -rection to provide a free space therebetween and permanently associated with each other, said free space being so located and proportioned as to induce concrete with which the joint is associated to crack at said free space.

In testimony that I claim the foregoing I hereunto afiix my signature. g y 1 v BENGT F. FRIBERG. 

